Flushable moist wipe or hygiene tissue and a method for making it

ABSTRACT

A flushable moist wipe or hygiene tissue including a hydraulically entangled nonwoven material impregnated with a wetting composition is provided. The nonwoven material contains at least 70%, by fibre weight, pulp fibres and at least 5%, by fibre weight, poly(lactic acid) fibres having a length between 8 and 20 mm and a fineness between 0.5 and 3 dtex. The poly(lactic acid) fibres are non-melted, and the moist wipe or hygiene tissue is free from added binders and wet-strength agents.

CROSS-REFERENCE TO PRIOR APPLICATION

This application is a §371 National Stage Application of PCT International Application No. PCT/SE2012/050832 filed on Jul. 12, 2012, which claims priority to U.S. Provisional Application No. 61/511,580 filed on Jul. 26, 2011, both of which are incorporated herein in their entirety.

TECHNICAL FIELD

The present disclosure refers to a moist wipe or hygiene tissue including a hydraulically entangled nonwoven material impregnated with a wetting composition. It is especially related to moist toilet paper and other wipes or hygiene tissue intended to be flushable in a sewer. It further refers to a method for making the flushable moist wipe or hygiene tissue.

TECHNICAL BACKGROUND

Pre-moistened wipes or hygiene tissue, are commonly used for cleansing different parts of the human body. Examples of specific uses are baby care, hand wiping, feminine care and toilet paper or a complement to toilet paper.

Since a long period of time often elapses from the time of manufacture of pre-moistened wipes until the time of use, they must have a sufficient structural integrity for their intended wiping function during such period. Adding a wet strength agent to the wipe will provide such wet integrity. However, especially when used as toilet paper, there is a strong desire that the wipe or tissue can be flushed in the sewer without causing problems with blocked pipes and filters. Wipes or tissue having a high wet strength will not disintegrate or break up into small fibre clumps when flushed in conventional household toilet systems, which may cause plugging of the drainage system.

Most moist flushable pre-moistened toilet papers which are on the market today are flushable due to their small size. They can move along the drainage and sewage pipes, but are not readily dispersible and may therefore cause problems with blocked pipes and filters.

It is previously known, for example through U.S. Pat. No. 3,554,788 to use an adhesive having a water-soluble component as a bonding agent in a water dispersible nonwoven material. The material is told to have a good dry strength but readily disperses in water and is flushable. This nonwoven material is packaged in dry condition and would not retain sufficient structural integrity for any longer period of time as is required for wet wipes.

A wet wipe made of a hydroentangled three ply sandwich structure comprising outer layers of synthetic fibres and a middle layer of cellulosic fibres is known through U.S. Pat. No. 6,110,848.

EP 1 320 458 B1 discloses a wet wipe capable of disintegrating under mild agitation in water and comprising at least 50% by weight cellulose fibres, at least 5% by weight manmade high crystallinity cellulose fibres and at least 0.5% by weight binder fibres. The fibres are hydroentangled and the binder fibres create a network that after activation and fusing lightly bonds the pulp fibres and high crystallinity cellulose fibres together.

U.S. Pat. No. 5,935,880 discloses a dispersible wet wipe comprising a hydroentangled fibrous web containing pulp fibres, optionally synthetic fibres and a binder composition, said binder composition comprises a divalent ion inhibitor, which facilitates the disintegration process.

EP 0 303 528 Al discloses a hydroentangled disintegratable nonwoven fibrous web used as a wet wipe. It comprises at least 70 weight % pulp fibres and at least 5 weight % staple length regenerated cellulose fibres.

U.S. Pat. No. 6,670,521 discloses a flushable wet wipe comprising a fibrous web having mechanically weakened regions. The fibrous web comprises at least 50 weight % cellulose fibres and may further contain poly(lactic acid) fibres. The web contains a wet strength agent.

There is still a need for a moist wipe or hygiene tissue which has sufficient structural integrity for its intended wiping function but which is readily disintegratable when flushed in a sewer.

SUMMARY

It is desired to provide a moist wipe or hygiene tissue intended to be flushable in a sewer. In a first aspect, there is disclosed a moist wipe or hygiene tissue including a hydraulically entangled nonwoven material impregnated with a wetting composition. The nonwoven material contains at least 70%, by fibre weight, pulp fibres, wherein said moist wipe or hygiene tissue includes at least 5%, by fibre weight, poly(lactic acid) fibres having a length between 8 and 20 mm and a fineness between 0.5 and 3 dtex. The poly(lactic acid) fibres are non-melted, and the moist wipe or hygiene tissue is free from added binders and wet-strength agents.

The moist wipe or hygiene tissue may comprise up to 10%, by fibre weight, regenerated cellulose staple fibres and/or natural fibers having a fibre length of at least 4 mm.

The poly(lactic acid) fibres may have a length between 12 and 18 mm.

The poly(lactic acid) fibres may have a fineness between 1 and 2 dtex.

The poly(lactic acid) fibres may be monocomponent fibres having a melting point of at least 140° C.

The moist wipe or hygiene tissue may have a basis weight between 40 and 100 g/m², wherein the basis weight is calculated on the nonwoven material without the wetting composition.

The moist wipe or hygiene tissue may be a moist toilet paper.

The moist wipe or hygiene tissue may have a wet strength in cross direction between 25 and 200 N/M, or between 40 and 200 N/m.

The poly(lactic acid) fibres may form an open interlaid structure mechanically bonded to the pulp fibers and the optional regenerated cellulose staple fibers and/or natural fibres.

The poly(lactic acid) fibres may have a modulus according to ASTM method D2256/D3822 of between 20 and 50 g/denier, or between 30 and 40 g/denier.

In a second aspect, there is disclosed a method of making a moist wipe or hygiene tissue comprising the steps of: foam-forming a fibre mixture of at least 70%, by fibre weight, pulp fibres and at least 5%, by fibre weight, poly(lactic acid) fibres having a length between 8 and 20 mm and a fineness between 0.5 and 3 dtex, hydroentangling said mixture to form a hydroentangled nonwoven web, and drying said web. The web is free from added binders and wet-strength agent, and the poly(lactic acid) fibres are non-melted, and impregnating the web with a wetting composition.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a microscope picture of a hydroentangled nonwoven web according to an embodiment of the invention.

FIG. 2 illustrates flushability tests performed with four hydroentangled moist wipe materials as described below.

DETAILED DESCRIPTION OF EMBODIMENTS

A premoistened wipe or hygiene tissue includes a hydroentangled nonwoven material impregnated with a wetting composition. The wetting composition may contain a major proportion of water and other ingredients depending on the intended use. Wetting compositions useful in moist wipes and hygiene tissue are well-known in the art.

Hydroentangling or spunlacing is a technique for forming a nonwoven web introduced during the 1970'ies, see e g CA patent no. 841 938. The method involves forming a fibre web, which is either drylaid or wetlaid, after which the fibres are entangled by means of very fine water jets under high pressure. Several rows of water jets are directed against the fibre, web which is supported by a movable foraminous support or a perforated drum. In this process, the fibres entangle with one another providing sufficient bonding strength to the fibrous web without the use of chemical bonding agents. The entangled fibrous web is then dried. The fibres that are used in the material can be natural fibres, especially cellulosic pulp fibres, manmade staple fibres, and mixtures of pulp fibres and staple fibres. Spunlace materials can be produced with high quality at a reasonable cost and they possess a high absorption capacity.

The fibres used in the moist wipe or hygiene tissue are at least 70%, by fibre weight, pulp fibres and at least 5%, by fibre weight, poly(lactic acid), PLA, fibres having a length between 8 and 20 mm and a fineness between 0.5 and 3 dtex. The PLA fibres may have a modulus between 20 and 50 g/denier, or between 30 and 40 g/denier, according to ASTM method D2256/D3822.

Optionally other manmade staple fibres may be included. In certain embodiments, manmade staple fibres are biodegradable, such as regenerated cellulose fibres, e.g. viscose, rayon and lyocell. The nonwoven web may contain up to 10% by fibre weight of such manmade staple fibres, other than PLA fibres. The length of these manmade fibres may be in the range of 4 to 20 mm. Other natural fibres than pulp fibres may also be included in the fibrous web, such as cotton fibres, sisal, hemp, ramie, flax etc. These natural fibres usually have a length of more than 4 mm.

Cellulose pulp fibres can be selected from any type of pulp and blends thereof. In particular embodiments, the pulp is characterized by being entirely natural cellulosic fibres and can include wood fibres as well as cotton. In particular embodiments, the pulp fibres are softwood papermaking pulp, although hardwood pulp and non-wood pulp, such as hemp and sisal may be used. The length of pulp fibres may vary from less than 1 mm for hardwood pulp and recycled pulp, to up to 6 mm for certain types of softwood pulp. Pulp fibres are advantageous to use since they are inexpensive, readily available and absorbent.

PLA is a hydrophobic polymer prepared from renewable agricultural raw materials. Fibres made of PLA are thus also hydrophobic and are considered to be non absorbent. As only minor amount of water is absorbed no major plasticizing (softening) effect is obtained and the wet flexural modulus of the PLA fibre is essentially the same as the dry flexural modulus and the PLA fibres are relatively stiff also in water.

For cellulosic based fibers like wood pulp, cotton, viscose, rayon or lyocell water is absorbed by the fibres. The wet flexural modulus thus collapse and the fibers become very flexible in water. Because of the low wet flexural modulus, these types of fibers have a tendency to entangle and bind with each other in the pulper if fiber length is too long. For pulp fibres this is not a problem due to its relatively short fibre lengths in the range of 0.5-2 mm. Pulp fibres can thus be used at high concentrations in the fibre mixtures.

Man-made regenerated cellulose fibers like viscose, rayon or lyocell are used at longer lengths in order to increase strength in the hydroentangled material. The longer the fibres are, and the higher the concentration is, the better reinforcing effect is obtained. Because of the low wet flexural modulus, these fibers are very effective in creating strength by hydroentanglement bonding. However, it is experienced that with too much regenerated cellulose fibers entanglement already occur in the pulper and poor runability and formation of the material is obtained. Shorter regenerated cellulose fibres are easier to process. For that reason it is important to balance the regenerated cellulose fibre length and fibre concentration considering the formation and desired strength.

When a wet web is able to be formed with pulp fibres and PLA fibres of relatively long length it is believed that a relatively open network of interlaid PLA fibres is formed. The pulp fibres will fill the space between and around the PLA fibres. Without any hydroentanglement, the wet strength of this material is poor. By the hydroentanglement, the pulp is interwined with the long PLA fibres and especially the interwinings at PLA fibre crossings creates strength in the material. By knitting the material together at the PLA fibre crossings a fibre network is obtained with a structural integrity allowing the material to be used in pre-moistened applications. The strength obtained in the material is created due to mechanical bondings/interlockings between pulp and the long PLA fibres. At entanglement of materials with a high pulp dosing, the entanglement energy must however be on a relatively low level so that the pulp is not flushed away from the web. For materials produced for applications such as moist wipes intended to be flushable in a sewer, the entanglement energy must also be balanced and kept on a relatively low level to secure a good disintegration. For that reason it is not believed that any major entanglement between PLA fibres occurs at low hydroentanglement energy levels. The hydroentanglement is also believed to compress certain areas in the structure and here the short, fine and mobile pulp fibres may work as a wedge. This is also believed to contribute to the strength of the material.

FIG. 1 is showing an image obtained with a Scanning Electron Microscope (SEM) of a hydroentangled material made with PLA and pulp fibres. The reinforcing network structure created by the PLA fibers is shown as well as the shorter and mobile cellulosic pulp fibers that have entangled and filled up the spaces between the PLA fibers. This image supports the theory described above.

By also using regenerated cellulose fibres together with PLA fibres and pulp fibres it has unexpectedly been shown that it might be easier to balance and control the structural integrity and strength required for a material to be used as a moist wipe, intended to be flushable in a sewer. Longer regenerated cellulose fibres will take part in the interlaid fibre network together with the PLA fibres, however differently. As for the PLA-pulp composite material, the pulp fibres will fill the space between and around the PLA and regenerated cellulose fibres. At hydroentanglement, the pulp fibres will create strength as described above for the PLA and pulp composite. By the low wet flexural modulus of the regenerated cellulose fibres, it is believed that they will entangle to a higher degree than the PLA fibres at the low hydroentanglement energy levels. The regenerated cellulose fibres may thus also entangle with each other and with PLA fibres to create strength.

By combining PLA fibres, regenerated cellulose fibres and pulp it is thus possible to balance the strength that the product become flushable i.e. disintegrates in a sewer. At the same time, the wet tensile strength is high enough that the product does not break at dispensing and during the wet wipe use. Surprisingly, sufficient wet strength is thus obtained for the hydroentangled composite material without any thermal bonds between PLA staple fibres or without use of any chemical binders.

The PLA fibers may, according to one embodiment, have a length between 12 and 18 mm.

The PLA fibres are non-melted so that the reinforcing network may be broken when the web is flushed in a sewer, for example. This will make the web to disintegrate.

The mechanical strength of a hydroentangled staple fibre-pulp composite material is a function of staple fibre concentration, staple fibre length, staple fibre coarseness, staple fibre flexural modulus, input of hydroentanglement energy as well as a function of the formation, including how the fibres are aligned in the structure. The material strength in the machine direction is always higher compared to the cross directional strength because of the alignment of the fibers in the direction of manufacture, due to the hydrodynamic shear as the sheet is formed, as well as because of the stress exerted on the material at web transfer through hydroentanglement and drying to the rewinder. In a simple fibre network approach it is usually considered that the number of fiber crossings can be described by simple probability distributions.

In an attempt to characterize the network structure created by the PLA fibres a theoretical value of number of crossover points between the PLA fibres can be calculated as described below.

For a web having a basis weight of 60 g/m² and a concentration of PLA fibres of 5 weight % the amount of PLA fibres will be 3 g/m². For PLA fibres having a fineness of 1.5 dtex (1.5 g/10 000 m) the total fibre length PLA fibres will be 20 000 m for 1 m² web. Half total fibre length is 10 000 m/m². The distance between fibres in mm is calculated by dividing 1000 (mm) with half the total fibre length, which in the above example will be 0.1 mm. By dividing the actual fibre length with this distance a theoretical value of number of crossover points can be obtained. The number of crossover points shows a linear relationship with the actual fibre length and with the concentration of PLA fibres and is illustrated in Table 1 below.

TABLE 1 Theoretical number of crossover points as a function of fibre length and fibre concentration for 1.5 dtex PLA fibres Fibre conc. (wt %) Fibre length (mm) 5 10 15 25 8 80 160 240 400 12 120 240 360 600 18 180 360 540 900

The PLA fibres may have a melting temperature of at least 140° C. so that they will withstand normal drying processes without softening or melting. In particular embodiments, the PLA fibres are monocomponent fibres. The moist wipe or hygiene tissue should be free from added binders and wet strength agents. Addition of binders and wet strength agents will deteriorate the flushability of the wipe since it makes it more difficult to break up and disperse in a sewer. Even small amount of wet strength agents may have big effects on the flushability.

PLA fibres are wettable and biodegradable, which is an advantage for their use in a moist wipe or hygiene tissue intended to be disposed after use.

The PLA fibres, pulp fibres and optional other fibres are mixed and formed into a fibrous web. The fibrous web can be foam formed, which is a variant of a wet-laying process. A surfactant is added to a dispersion of the fibres in a liquid, normally water. The foamed fibre dispersion is deposited on a foraminous support member where it is dewatered to form a continuous web-like material. The fibre dispersion may be diluted to any consistency that is typically used in conventional papermaking process. A very even fibre distribution is achieved in a foam forming process and it is also possible to use longer fibres than in a conventional wet-laying process.

The formed fibrous web is then subjected to hydroentanglement from several rows of manifolds, from which water jets at a high pressure are directed towards a fibrous web, while this is supported by the foraminous support member. The fibrous web is drained over suction boxes. Thereby, the water jets accomplish an entanglement of the fibrous web, i.e. an intertwining of the fibres. Appropriate pressures in the entanglement manifolds are adapted to the fibrous material, grammage of the fibrous web, etc. In particular embodiments, the entangling energy is relatively low to ensure that the fibres in the web are not too strongly entangled, but that the web will be disintegratable as desired. The water from the entanglement manifolds is removed via the suction boxes and is pumped to a water purification plant, and is then re-circulated to the entangling stations.

For a further description of the hydroentanglement or, as it is also called, spunlacing technology, reference is made e.g. to CA patent No. 841 938.

Hydroentangling may occur in one or several steps and from one side of the web or from both sides thereof. The web may be transferred to another foraminous support between two subsequent hydroentangling steps.

The entangled material is dewatered and brought to a drying station for drying before the finished material is reeled up and converted. Drying can be performed by blowing hot air through the fibrous web, by IR dryers or other non-compacting drying technique.

The entangled web is converted into wipes or hygiene tissue of appropriate dimensions.

The wet strength in the cross-machine direction should be between 25 and 200 N/m, or between 40 and 200 N/m. The wet strength in machine direction is usually higher. The wet strength is measured with water according to the test method SS-EN ISO12625-5:2005.

In certain embodiments, the basis weight of the wipe or hygiene tissue is between 40 and 100 g/m² as calculated on the dry weight of the fibrous material, excluding the wetting composition.

The relatively low strength at least in cross-machine direction may be accomplished by controlling the hydroentangling process, for example the pressure in the entanglement manifolds and/or the web speed through the process. Thus by lowering the pressure in the entanglement manifolds and/or increasing the speed through the process, the strength properties of the hydroentangled web will usually be lowered, especially the strength in the cross-machine direction. The strength in the machine direction will always be higher due to the fibre orientation and not effected by the hydroentangling process to the same extent as the cross-machine direction strength. It is also known that the fibre orientation in machine direction can be effected during the formation of the fibre web by controlling the speed of the jet of the fibre dispersion from the inlet box relative to the speed of the forming wire.

The wipe or hygiene tissue may be creped, embossed or otherwise textured to enhance softness of the product. Normally, working the web to enhance softness tends to reduce the wet strength of the web.

The wipe or hygiene tissue is impregnated with a wetting composition containing ingredients depending on the intended use of the product. A major proportion of the wetting composition is normally water. Other ingredients may include cleansing agents, skin care agents, bactericides, fungicides, emollients, perfumes, preservatives etc. depending on the intended use.

The ingredients in the wetting composition will also influence the wet strength as well as the disintegration of the moist wipe. Most likely ingredients such as cleansing agents and emollients will decrease the wet strength and favour the disintegration of the product.

One use of the wipe or hygiene tissue is as a moist toilet paper. As an example a suitable wetting composition in a moist toilet paper may be aqueous based and may contain ingredients like propylene glycol, phenoxy ethanol, coco-glycocide, polyaminopropyl biguanide, dehydroacetic acid, perfume, cocoamidopropyl betaine, chamomilla recutita, bisabolol, citric acid, amylcinnamal, citonellol, hexylcinnamaldehyd, butylphenylmethylpropional and the like.

The moist wipe or hygiene tissue is either individually packed in a sealed package that can be torn open by the user, or a dispenser containing a large number of wipes or tissue that may be dispensed through a dispenser opening in the dispenser.

EXAMPLE

Embodiments of the invention are further illustrated by the enclosed test results. PLA fibres at a length of 12.7 and 18 mm were supplied by Fibre Innovation Technology (Johnson City, Tenn., US). Lyocell fibres i.e. regenerated cellulose fibres at a length of 12 mm were supplied by Lenzing. Pulp fibres were supplied by International Paper.

The pulp and staple fibre compositions were wet laid onto a forming wire with a Fourdrinier headbox. Hydroentanglement was made with multiple hydroentanglement heads using an entangling energy in the range between 60 and 150 kWh/ton. After hydroentanglement the material was dried by through air drying technology. For material 4, 0.3 weight-% wet strength agent was added to the material after the entanglement by spraying.

For materials 1-3, no chemical binder was used, a sufficient CD wet strength was obtained and materials were disintegrated with the tipping tube method. For material 4 were 0.3% wet strength agent was added to the material no disintegration was obtained by the tipping tube method.

The following test methods were used: Basis weight: SS-EN-ISO 12625-6:2005; Dry strength: SS-EN-ISO 12625-4:2005; Wet strength: SS-EN ISO12625-5:2005 (measured in water).

TABLE 2 Material composition Material 1 2 3 4 18 mm PLA (%) 18 18 — — 12.7 mm PLA (%) — — 10 10 12 mm Lyocell (%) — — 10 10 Pulp (%) 82 82 80 79.7 Wet strength agent (%) 0 0 0 0.3

TABLE 3 Test results Material 1 2 3 4 Basis weight (g/m²) 68.2 66.5 73.4 73.7 Thickness (μm) 631 618 572 577 Tensile strength wet MD (N/m) 173 247 305 330 Tensile strength wet CD (N/m) 52 48 160 134

The disintegration of the material in the form of a sheet 18.5×12 cm is illustrated in the form of photos taken after 480 rotations in a tipping tube according to EDANA flushability test and is shown in FIG. 2, wherein photo 1) represents material 1, photo 2) represents material 2 etc. 

1. A flushable moist wipe or hygiene tissue comprising a hydraulically entangled nonwoven material impregnated with a wetting composition, said nonwoven material containing at least 70%, by fibre weight, pulp fibres, wherein said moist wipe or hygiene tissue comprises at least 5%, by fibre weight, poly(lactic acid) fibres having a length between 8 and 20 mm and a fineness between 0.5 and 3 dtex, said poly(lactic acid) fibres are non-melted, and wherein the moist wipe or hygiene tissue is free from added binders and wet-strength agents.
 2. A moist wipe or hygiene tissue as claimed in claim 1, wherein said moist wipe or hygiene tissue comprises up to 10%, by fibre weight, regenerated cellulose staple fibres and/or natural fibers having a fibre length of at least 4 mm.
 3. A moist wipe or hygiene tissue as claimed in claim 1 wherein the poly(lactic acid) fibres have a length between 12 and 18 mm.
 4. A moist wipe or hygiene tissue as claimed in claim 1, wherein the poly(lactic acid) fibres have a fineness between 1 and 2 dtex.
 5. A moist wipe or hygiene tissue as claimed in claim 1, wherein the poly(lactic acid) fibres are monocomponent fibres having a melting point of at least 140° C.
 6. A moist wipe or hygiene tissue as claimed in claim 1, wherein said moist wipe or hygiene tissue has a basis weight between 40 and 100 g/m².
 7. A moist wipe or hygiene tissue as claimed in claim 1, wherein said moist wipe or hygiene tissue is a moist toilet paper.
 8. A moist wipe or hygiene tissue as claimed in claim 1, wherein said moist wipe or hygiene tissue has a wet strength in cross direction between 25 and 200 N/m.
 9. A moist wipe or hygiene tissue as claimed in claim 1, wherein the poly(lactic acid) fibres form an open interlaid structure mechanically bonded to the pulp fibers and the optional regenerated cellulose staple fibers and/or natural fibres.
 10. A moist wipe or hygiene tissue as claimed in claim 1, wherein the poly(lactic acid) fibres have a modulus according to ASTM method D2256/D3822 of between 20 and 50 g/denier.
 11. A method of making a moist wipe or hygiene tissue comprising the steps of: foam-forming a fibre mixture of at least 70%, by fibre weight, pulp fibres and at least 5%, by fibre weight, poly(lactic acid) fibres having a length between 8 and 20 mm and a fineness between 0.5 and 3 dtex, hydroentangling said mixture to form a hydroentangled nonwoven web, drying said web, wherein said web is free from added binders and wet-strength agent, and wherein the poly(lactic acid) fibres are non-melted, and impregnating the web with a wetting composition.
 12. The method as claimed in claim 11, wherein the fibre mixture comprises up to 10%, by fibre weight, manmade staple fibres other than poly(lactic acid) fibres.
 13. The method as claimed in claim 11, wherein the poly(lactic acid) fibres have a length between 12 and 18 mm.
 14. The method as claimed in claim 11, wherein the poly(lactic acid) fibres have a fineness between 1.5 and 2 dtex.
 15. The method as claimed in claim 11, wherein that the poly(lactic acid) fibres are monocomponent fibres having a melting point of at least 140° C. 